a) Field of the Invention
The invention is directed to an arrangement for the measurement of optical radiation of radiation sources, especially radiation power.
b) Description of the Related Art
Power measuring devices for measuring optical radiation of radiation sources, especially also of laser radiation sources, can vary, for example, between power measuring devices for directionally radiating sources, also called power meters, such as bolometers, photodiodes, and power measuring devices for diffusely radiating sources (high-divergence sources) such as Ulbricht spheres.
Both types, both diffusely and directionally radiating fiber applicators with lengths of up to 10 cm and diameters up to 20 mm, are used in photodynarric therapy (PDT). Knowledge of the radiation power delivered by the applicator being used is crucial for the successful course and conclusion of treatment. At the present time, the principle of Ulbricht spheres is applied for power measurement.
An Ulbricht sphere of the type mentioned above is described in "ABC der Optik [The ABC's of Optics]", VEB Brockhaus Verlag, Leipzig, 1961, 484-485, in connection with luminous flux meters. This Ulbricht sphere is constructed in such a way that the most uniform possible distribution of the emitted radiation takes place in the interior of the sphere. A part of the diffusely reflected radiation is converted by a suitable detector whose receiver surface is small in comparison to the inner surface of the sphere, e.g., by a photodiode, into an electric signal which is proportional to the radiation output. Further, this measuring device is disadvantageous in that the measurement values are also dependent on the size of the radiation sources to be measured and on their position in the sphere.
For this reason, in order to suppress possible radiation characteristics of expanded radiation sources, the Ulbricht sphere must be as large as possible, the inner surface must reflect as diffusely as possible, and the receiver must be small in comparison to the inner surface and must be protected from direct radiation. Taking into account the requirement for measurement of the above-mentioned applicators with a length of 10 cm and a diameter of 20 mm, an Ulbricht sphere necessary for this purpose is difficult to integrate in an existing device or device design already by virtue of its size and, moreover, increases the cost of manufacture.